rsautl(1ssl)rsautl(1ssl)NAMErsautl - RSA utility
SYNOPSIS
openssl rsautl [-in filename] [-out filename] [-inkey filename]
[-pubin] [-certin] [-sign] [-verify] [-encrypt] [-decrypt] [-pkcs]
[-ssl] [-raw] [-hexdump] [-asn1parse]
OPTIONS
Specifies the input filename to read data from or standard input if
this option is not specified. Specifies the output filename to write
to or standard output by default. Input key file. By default it should
be an RSA private key. The input file is an RSA public key. The input
is a certificate containing an RSA public key. Signs the input data
and outputs the signed result. This requires and RSA private key. Ver‐
ifies the input data and output the recovered data. Encrypts the input
data using an RSA public key. Decrypts the input data using an RSA
private key. The padding to use: PKCS#1 v1.5 (the default), PKCS#1
OAEP, special padding used in SSL v2 backwards compatible handshakes,
or no padding, respectively. For signatures, only -pkcs and -raw can be
used. Hex dumps the output data. Asn1parses the output data. This is
useful when combined with the -verify option.
DESCRIPTION
The rsautl command can be used to sign, verify, encrypt and decrypt
data using the RSA algorithm.
NOTES
Because rsautl uses the RSA algorithm directly, it can only be used to
sign or verify small pieces of data.
EXAMPLES
Sign some data using a private key:
openssl rsautl-sign -in file -inkey key.pem -out sig
Recover the signed data
openssl rsautl-verify -in sig -inkey key.pem
Examine the raw signed data:
openssl rsautl-verify -in file -inkey key.pem -raw -hexdump
0000 - 00 01 ff ff ff ff ff ff-ff ff ff ff ff ff ff ff
................
0010 - ff ff ff ff ff ff ff ff-ff ff ff ff ff ff ff ff
................
0020 - ff ff ff ff ff ff ff ff-ff ff ff ff ff ff ff ff
................
0030 - ff ff ff ff ff ff ff ff-ff ff ff ff ff ff ff ff
................
0040 - ff ff ff ff ff ff ff ff-ff ff ff ff ff ff ff ff
................
0050 - ff ff ff ff ff ff ff ff-ff ff ff ff ff ff ff ff
................
0060 - ff ff ff ff ff ff ff ff-ff ff ff ff ff ff ff ff
................
0070 - ff ff ff ff 00 68 65 6c-6c 6f 20 77 6f 72 6c 64 .....hello
world
The PKCS#1 block formatting is evident from this. If this was done
using encrypt and decrypt the block would have been of type 2 (the sec‐
ond byte) and random padding data visible instead of the 0xff bytes.
It is possible to analyze the signature of certificates using this
utility in conjunction with asn1parse. Consider the self-signed example
in certs/pca-cert.pem. Running asn1parse yields the following:
openssl asn1parse -in pca-cert.pem
0:d=0 hl=4 l= 742 cons: SEQUENCE
4:d=1 hl=4 l= 591 cons: SEQUENCE
8:d=2 hl=2 l= 3 cons: cont [ 0 ]
10:d=3 hl=2 l= 1 prim: INTEGER :02
13:d=2 hl=2 l= 1 prim: INTEGER :00
16:d=2 hl=2 l= 13 cons: SEQUENCE
18:d=3 hl=2 l= 9 prim: OBJECT :md5WithRSAEncryption
29:d=3 hl=2 l= 0 prim: NULL
31:d=2 hl=2 l= 92 cons: SEQUENCE
33:d=3 hl=2 l= 11 cons: SET
35:d=4 hl=2 l= 9 cons: SEQUENCE
37:d=5 hl=2 l= 3 prim: OBJECT :countryName
42:d=5 hl=2 l= 2 prim: PRINTABLESTRING :AU
....
599:d=1 hl=2 l= 13 cons: SEQUENCE
601:d=2 hl=2 l= 9 prim: OBJECT :md5WithRSAEncryption
612:d=2 hl=2 l= 0 prim: NULL
614:d=1 hl=3 l= 129 prim: BIT STRING
The final BIT STRING contains the actual signature. It can be extracted
using the following command:
openssl asn1parse -in pca-cert.pem -out sig -noout -strparse 614
The certificate public key can be extracted using the following com‐
mand: openssl x509 -in test/testx509.pem -pubout -noout >pubkey.pem
The signature can be analyzed with:
openssl rsautl-in sig -verify -asn1parse -inkey pubkey.pem -pubin
0:d=0 hl=2 l= 32 cons: SEQUENCE
2:d=1 hl=2 l= 12 cons: SEQUENCE
4:d=2 hl=2 l= 8 prim: OBJECT :md5
14:d=2 hl=2 l= 0 prim: NULL
16:d=1 hl=2 l= 16 prim: OCTET STRING
0000 - f3 46 9e aa 1a 4a 73 c9-37 ea 93 00 48 25 08 b5
.F...Js.7...H%..
This is the parsed version of an ASN1 DigestInfo structure. The digest
used was md5. The part of the certificate that was signed can be
extracted with the following command:
openssl asn1parse -in pca-cert.pem -out tbs -noout -strparse 4
Its digest can be computed with the following command:
openssl md5 -c tbs
MD5(tbs)= f3:46:9e:aa:1a:4a:73:c9:37:ea:93:00:48:25:08:b5
This agrees with the recovered value above.
SEE ALSO
Commands: dgst(1ssl), rsa(1ssl), genrsa(1ssl)rsautl(1ssl)
